Season 4

A 7-year-old girl contracts the bubonic plague and suffers a 107 fever, vomiting, painful buboes, and seizures; a yoga instructor finds out that what she thought was influenza is actually necrotizing fasciitis caused by Streptococcus intermedius and Peptostreptococcus; a state wrestling champion contracts angiostrongyliasis.

A teenage ballerina suffers from painful migraines and muscle failures; a young missionary's skin crawls when he uncovers an unholy revelation.

A newly engaged Illinois man mysteriously collapses and suffers organ failure and gangrene from Legionnaire's disease. His fiance gazes in horror as he must choose between life and limb; a perky animal-loving eight-year-old girl survives rabies – a disease with a 99% fatality rate; a college freshmen almost goes blind from a bout of Acanthamoeba keratitis.

A mother suffers with abdominal pain and nausea for four years until the true cause of her condition is discovered; a 2-year-old girl develops a mysterious lump on her neck.

A small-town boy's summer fun is cut short by a life-threatening Neisseria meningitidis infection. An oil rig worker and daredevil experiences sensitivity to light, muscle pain and horrifying hallucinations from Trichinella spiralis after eating bear meat. A former beauty queen suffers an extreme case of asthma for one year from a nasal packing contaminated with Aspergillus niger fungi.

A Peace Corps volunteer traveling to Burkina Faso suddenly suffers from excruciating bouts of nausea and diarrhea from Entamoeba histolytica, and must find medical help before it is too late; a young woman almost suffocates due to hantavirus pulmonary syndrome she got from breathing dust while cleaning up contaminated with mouse feces; an 18-month-old boy gets infected with Baylisascaris procyonis worms which cause his brain to swell and have neurological damage, eye fluttering, and unresponsiveness.

A teenager caught in the 2011 Joplin tornado in Missouri is recovering in the hospital when he suddenly suffers from a life-threatening case of zygomycosis. A couple traveling who visited South Africa get maggots under their skin; a man suffers coughing fits, severe headaches, vertigo, and violent episodes (including chasing his son with a wrench and punching him in the face) before doctors discover the fungus Cryptococcus neoformans has infected his brain.

A teenage boy develops stomach pains, starts vomiting blood and fecal matter, and has nausea from accidentally swallowing a bristle from a grill brush, which got lodged in his intestines; in 2011, a 16-year-old girl who swam in a Florida river experiences a headache, fever, vomiting, mental confusion, unusual behavior and dies from amoebic meningitis; an industrial painter has difficulties breathing and walking from Blastomyces dermatitidis.

A special episode with three cases that happened during the holidays – A newlywed woman gets a constant pain in her scalp from botfly larvae; a Virginia man gets sharp back pains and develops a hole in his heart from Streptococcus viridans; a female business consultant and part-time photographer gets valley fever.

A newborn baby develops hydrocephalus from a parasitic disease called toxoplasmosis, which was contracted from his mother; an 11-year-old boy suffers headaches, vomiting, seizures, and starts speaking gibberish from being infected with the eastern equine encephalitis virus; a teenager living on a farm suffers a severe cough and fever from Paragonimus kellicotti.